1. Field of the Invention
The present invention relates to a platinum/alkenylsiloxane complex catalyst composition that is a useful hydrosilylation reaction catalyst. More particularly, the present invention relates to an improved platinum-alkenylsiloxane complex catalyst composition for which the catalytic activity of the platinum-alkenylsiloxane complex does not change during longterm storage of the composition.
2. Description of the Prior Art
The hydrosilylation reaction involves addition of an organohydrogensiloxane across an unsaturated bond, for example, a carbon-to-carbon double bond. Compared with peroxide-based curing reactions and curing reactions involving the condensation of silicon-bonded hydrolyzable groups with silanol groups, the hydrosilylation reaction offers the advantages of a relatively rapid curing rate and no reaction by-products. As a consequence, it is widely utilized as the curing reaction in curable organopolysiloxane compositions.
Various transition metal compounds are known in the art as catalysts of hydrosilylation reactions, platinum compounds being the most widely utilized class of catalysts. Among these platinum compounds chloroplatinic acid-alkenylsiloxane complexes are known to have high catalytic activity (for example, refer to U.S. Pat. No. 3,419,593, which issued to Willing on Dec. 31, 1968).
Also known are catalyst compositions in the form of pastes prepared by blending an organopolysiloxane and microparticulate hydrophilic silica together with a chloroplatinic acid-alkenylsiloxane complex. These paste compositions are widely used because they are easy to add and blend into curable organopolysiloxane compositions and thus are easy to use.
A shortcoming of platinum-alkenylsiloxane complexes is their relatively poor stability. These platinum present in these compositions readily converts to finely divided platinum metal (platinum black) with a resulting decline in catalytic activity. In particular, compositions containing both microparticulate hydrophilic silica and a platinum-alkenylsiloxane complex suffer from the problem of a substantial decrease in catalytic activity with time, as determined by the time required to cure a specified organosiloxane composition comprising a vinyl-substituted polyorganosiloxane and an organohydrogensiloxane.
The present inventor carried out various investigations in order to solve the problem of decreasing catalytic activity, and the present invention was developed as a result of these investigations.
The object of the present invention is to provide a composition comprising a finely divided silica filler and a platinum-alkenylsiloxane complex wherein the level of activity as a hydrosilylation reaction catalyst remains substantially constant as a function of time.